The basic structure of a microphone is generally well known and includes a diaphragm which vibrates in response to changes in acoustic pressure. The diaphragm is a thin polymer film which needs to be held under a certain amount of tension in order to provide a restoring force to move the diaphragm back towards the ring after it has been deflected. The diaphragm is typically attached to a ring 2, as illustrated in FIG. 1, within the microphone in order to provide the necessary tension. The deflection of the diaphragm in response to an acoustic pressure is inversely proportional to the tension. The output of the microphone is directly proportional to the deflection of the diaphragm. Therefore, the tension affects the sensitivity of the microphone. The function of the support ring is to provide a means of indefinitely maintaining a constant tension in the diaphragm.
The diaphragm film is fastened to the support ring at its perimeter, normally with adhesive. The support ring must provide adequate surface area for this bond such that the bond strength is sufficient to resist the tension in the diaphragm. The diaphragm has an area interior to the ring which is unsupported and free to move in response to acoustic pressure. In general, the microphone assembly is designed to maximize this area.
The diaphragm support ring is generally fastened to the microphone housing, thereby creating a sealed volume. The fastening is generally accomplished by adhesive, which forms a layer between the relatively rigid microphone housing and the diaphragm support ring. In some cases, the adhesive can react to changes in ambient conditions (temperature/humidity) by swelling or shrinking. The shrinking or swelling of adhesive can generate forces which push or pull on the diaphragm support ring. The support ring can be distorted or deflected by this stress. If the support ring is distorted it can result in a change in the diaphragm tension, which would be reflected in an undesirable and/or unpredictable change in the microphone's sensitivity.
A need, therefore, exists for a microphone assembly utilizing a ring which provides improved stability.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.